The present invention relates generally to a process for obtaining an ophthalmic lens comprising a surface utility microstructure and more particularly an antiglare microstructure.
Nowadays the most currently used means to impart antiglare properties to ophthalmic lenses, in particular in organic glass, is to coat on the lens a layer or a system of antiglare layers formed with mineral materials. The use of such antiglare layer in mineral materials has drawbacks in that it may modify the mechanical properties of the lens being obtained, and may modify more particularly the anti-abrasive properties of the hard anti-abrasive layers also coated on the ophthalmic lens.
Reaching optical properties from surface microstructures is a known art in optics. Thus, U.S. Pat. No. 5,630,902 discloses the transfer of a microstructure made with diffractive optical elements into a photopolymerizable material layer coated on a plastics substrate through die stamping, for example with the help of a quartz die supporting the desired microstructure.
U.S. Pat. No. 4,013,465 describes a process for producing a surface having a reduced reflection for electromagnetic radiation, having steps consisting in coating on a substrate surface a layer of a photosensitive material, exposing said material to a regular electromagnetic radiation pattern to which it is sensible and developing the sensible material so that the topography of the developed material surface corresponds to the light patterns so as to obtain a surface having a reduced reflection of the visible radiation.
GB-A-2,027,441 describes a process for producing an article comprising a monolithic plastics shaped layer or body consisting in some cross-linked polymers and comprising one or more surfaces bearing a microstructure replica, comprising the steps of filling a master mould bearing the microstructure with an oligomeric, cross-linkable, flowable fluidic composition being addition polymerizable with a radiation and having xe2x80x9chardxe2x80x9d and xe2x80x9csoftxe2x80x9d segments, and of exposing the cast composition to an actinic radiation so as to form the item. Said document discloses that the term microstructure encompasses discontinuities, such as projections and indentations, in the surface, the profile of which varies from a median or central line passing through the microstructure so that the sum of the surfaces being circumscribed by the surface profile above the line equals the sum of the surfaces below the line, said line being essentially parallel to the normal surface (bearing the microstructure) of the item. The height of such deviations varies from xc2x10.05 xcexcm to xc2x1750 xcexcm over a characteristic length representative of the surface, for example 1 to 30 cm. The medium profile or central line may be plane, concave, convex, aspherical or a combination of such shapes.
The items wherein such deviations are of a lower order, i.e. from xc2x10.005 xcexcm to 0.1 xcexcm or preferably xc2x10.05 xcexcm and such deviations are infrequent or appear minimally, i.e. the surface is free from any significant discontinuity, are those for which the microstructure-bearing surface is a xe2x80x9cflatxe2x80x9d or xe2x80x9cperfectly smoothxe2x80x9d surface. Such items are useful for example as precision optical elements or elements with a precision optical interface, including ophthalmic lenses. The items for which such deviations are of a lower order but appear frequently are those for example bearing utility discontinuities, like in the case of items having an antiglare microstructure. Items for which deviations are of a high order, i.e. from xc2x10.1 xcexcm to xc2x1750 xcexcm, to which a microstructure can be affected, comprising a set of utility discontinuities, that are identical or different, spaced apart or contiguous, randomly or orderly, are items such as back-reflective sheets, linear Fresnel lenses and video discs. Moreover, said document mentions that it can be necessary or desired to choose particular oligomeric compositions the hardening shrinkage of which is weak so as to avoid parasitic discontinuity occurrence interfering with the utility discontinuities.
The present invention has thus as an object a process for obtaining an ophthalmic lens, i.e. an item having a sight-correcting geometry, comprising a surface utility microstructure, i.e. having optical properties, in particular antiglare properties, the utility microstructure geometry being initially determined by an interferential process.
The present invention has also as an object said thus obtained lenses comprising a sight-correcting geometry surface provided with a utility microstructure, in particular having antiglare properties, the geometry of which is initially determined through an interferential process.
An object of the present invention is thus to provide a process for obtaining an ophthalmic lens, i.e. an item having a sight-correcting geometry comprising a surface utility microstructure, i.e. optical properties, in particular antiglare properties, the utility microstructure geometry being initially determined by an interferential process.
Another object of the present invention is also the so-obtained lenses comprising a sight-correcting geometry surface provided with a utility microstructure, in particular antiglare properties, the geometry of which is initially determined by an interferential process.
Such a utility microstructure may be realised in a surface of the lens itself or in a surface functional layer of the ophthalmic lens.
According to the invention, the process for obtaining an ophthalmic lens comprising a surface utility microstructure the geometry has been initially determined through an interferential process, comprises a step for transferring the microstructure from a mould an internal surface of which supports the microstructure and has a sight-correcting geometry.
Preferably, the sight-correcting geometry surface is a progressive geometry surface. Generally, the bend of the mould progressive geometry surface has a bending radius being measured at any point of the correcting surface comprised between 40 mm and 100 mm.
According to the present invention all conventional moulding types may be used to manufacture ophthalmic lenses such as direct moulding, for example through an integral mould or a composite mould, with added elements or with insert, or overmoulding, and the so-called xe2x80x9ctransferxe2x80x9d mouldings, for example by die-stamping, or with the well-known method in ophthalmic optics with xe2x80x9cIn-Mold Coatingxe2x80x9d transfer.
In a first embodiment of the invention, the mould being used is an integral mould, i.e. the utility microstructure is formed directly in an internal mould surface having the required sight-correcting geometry. The mould may be made with plastics, mineral glass or metal, particularly nickel.
In a second embodiment of the invention, the mould is a composite mould comprising an insert having a surface in which the utility microstructure is formed, said insert suiting to the mould surface having the sight-correcting geometry, so that the insert surface comprising the utility microstructure should also have the required sight-correcting geometry. The insert may be initially shaped so as to have the required sight-correcting geometry and be secured to the corresponding mould surface, for example with an adhesive. The insert may also have initially a plane shape and be then distorted to suit to the mould sight-correcting geometry surface. In this last case, the insert may also be secured to the mould sight-correcting geometry surface with an adhesive. When the microstructure-bearing insert is a plastic element adapted to be applied on a surface of a mould, said element must have a minimum elasticity is in the plane to be able to be correctly applied. Such convenient elements are polyurethane elements having for example a Young modulus measured at 30xc2x0 C. of 1.2 Gigapascals. Generally, said convenient elements have a lower Young modulus than 2.5 Gigapascals.
Finally, the insert may be made with a layer of such a material as a plastics directly formed on a surface of a substrate.
In a third embodiment of the invention, the mould is a composite mould comprising a plane insert provided with the utility microstructure on one of surfaces thereof, said plane insert being distorted in the mould to suit to the mould sight-correcting geometry surface by applying a pressure or a vacuum in the mould.
According to the process for obtaining ophthalmic lenses according to the invention, there may use all optical materials or compositions, being settable with heat or an actinic radiation, in particular a UV radiation, which can be cast or injected into the mould, and which lead to ophthalmic lenses with the required optical transparency and necessary mechanical properties. Such optical materials or compositions comprise not only the materials and compositions used to manufacture the ophthalmic lens itself, but also the materials and compositions allowing for the deposit of particular functional layers onto an ophthalmic lens, such as the materials adapted to form an anti-abrasive layer on an ophthalmic lens.
Preferably, the optical material or composition is a thermoplastic material or a liquid composition of monomers being settable with heat or an actinic radiation. The liquid monomer compositions are particularly recommended in the process according to the invention.
The monomers useful in the optical monomer compositions for use in the process according to the invention include alkyl (meth)acrylates, in particular C1-C4 alkyl (meth)acrylates such as methyl (meth)acrylate and ethyl (meth)acrylate, allyl derivates such as allyl carbonates of linear or branched, aliphatic or aromatic polyols, and thio(meth)acrylic derivates.
Particularly recommended monomers in the process according to the invention are the allyl carbonates of polyols including ethylene glycol bis allyl carbonate, diethylene glycol bis 2-methyl carbonate, diethylene glycol bis(allyl carbonate), ethylene glycol bis(2-chloro allyl carbonate), triethylene glycol bis(allyl carbonate), 1,3-propane diol bis(allyl carbonate), propylene glycol bis(2-ethyl allyl carbonate), 1,3-butane diol bis(allyl carbonate), 1,4-butane diol bis(2-bromo allyl carbonate), dipropylene glycol bis(allyl carbonate), trimethylene glycol bis(2-ethyl allyl carbonate), pentamethylene glycol bis(allyl carbonate), isopropylene bisphenol-A bis(allyl carbonate). A particularly recommended monomer is the diethylene glycol bis(allyl carbonate).
Another class of monomers convenient for compositions useful in the process of the invention comprises aromatic polyethoxylated (meth)acrylates such as the polyethoxylated bisphenol-A dimethacrylates, in particular those described in French patent application FR-A-2 699 541.
Thio(meth)acrylic monomers may also be used, in particular those described in French patent application FR-A-2 734 827.
Compositions based on polythiols and polyisocyanates in monomeric form may also be used, leading to polythiourethanes such as described for example in patent U.S. Pat. No. 4,689,387.
Finally, compositions may be used including one or more di- or polythiol monomers with one or more monomers bearing reactive unsaturated groups with thiol functions, such as vinyl, (meth)acrylic or thio(meth)acrylic groups.
Of course the monomer compositions may comprise mixtures of the above-mentioned monomers.
It is to be noticed that the higher the refraction index of the layer comprising the microstructure, the higher the antiglare effect. Consequently, the index of the microstructured layer is preferably is equal to or higher than 1.55, more preferably equal to 1.6 or more. Naturally, such microstructured layer may be formed with the organic glass or with a surface layer such as an anti-abrasion coating applied onto a surface of a substrate in organic glass.
Thermoplastic materials useful for the process according to the invention include thermoplastic prepolymers and polymers such as thermoplastic polycarbonates.
According to another aspect of the process of the invention, the utility microstructure is not formed in the ophthalmic lens itself, but in a functional coating applied on such lens, for example an anti-abrasion coating. In this case, in the process according to the invention, any monomer compositions may be used if they are convenient to form on an ophthalmic lens a layer having a particular property, such as an anti-abrasion coating for example.
Such abrasion-resistant settable compositions include the compositions based on a silane hydrolyzate, in particular on an epoxysilane hydrolyzate as described in French patent application 93 026 49, and the compositions based on acrylic derivates.
Naturally, the materials and compositions useful in the process according to the present invention may include any additive conventionally used for producing ophthalmic lenses, in particular thermal and/or photochemical polymerisation initiators and catalysts.
As indicated, the utility microstructure geometry is initially determined with an interferential process, i.e. the utility microstructure is either formed directly on the mould surface with an interferential process or obtained by transfer from a matrix a surface of which comprises a utility microstructure obtained with an interferential process.
More precisely, the interferential process consists in making a pattern of interference fringes by superimposing two coherent light waves, for example two laser beams, and irradiating a photosensitive material layer coated onto a substrate through such pattern of interference fringes.
Then, by developing conventionally the photosensitive material layer, a periodic microstructure is obtained.
Two irradiation steps for the photosensitive layer can be provided by rotating the substrate, preferably by 90xc2x0 after the first irradiation step, and then the photosensitive material layer is developed conventionally.
A periodic microstructure is then obtained in the plane. Thus, an isotropic structure may be obtained the antiglare properties are independent from the sight angle.
Naturally, patterns of interference fringes having different or identical pitches (i) and amplitudes (2A). Also said irradiation steps may be repeated various times so as to obtain after development a final microstructure formed with multiple superimposed microstructures.
Generally, the wavelength of the coherent light beams, for example laser beams, is comprised between 170 and 510 nm and the pitch of the pattern of interference fringes (and consequently of the periodic microstructure being obtained) is comprised between 100 and 300 nm. The amplitude 2A is comprised generally between 100 and 300 nm.
Preferably plane light waves are used and so a sinusoidal microstructure is obtained.
The periodic microstructure may be generally defined in an orthogonal reference system (x, y, z) with the following equation (1):                     z        =                              f            ⁡                          (                              x                ,                y                            )                                =                                                    ∑                                  n                  =                  1                                k                            ⁢                              xe2x80x83                            ⁢                              [                                                                            A                      n                                        ⁢                                          sin                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                      xe2x80x83                                                    ⁢                          n                          ⁢                                                      x                            i                                                                          )                                                                              +                                                            B                      n                                        ⁢                                          cos                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                      xe2x80x83                                                    ⁢                          n                          ⁢                                                      x                            i                                                                          )                                                                                            ]                                      +                                          ∑                                  m                  =                  1                                k                            ⁢                              xe2x80x83                            ⁢                              [                                                                            C                      m                                        ⁢                                          sin                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                      xe2x80x83                                                    ⁢                          m                          ⁢                                                      y                            i                                                                          )                                                                              +                                                            D                      m                                        ⁢                                          cos                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                      xe2x80x83                                                    ⁢                          m                          ⁢                                                      y                            i                                                                          )                                                                                            ]                                                                        (        1        )            
where An, Bn are Fourier coefficients in the microstructure in the direction x,
Cm, Dm are Fourier coefficients in the microstructure in the direction y, and
i is the pitch (period) of the microstructure.
Preferably, Bn=Dm=O, An=Cm=A (sinusoidal structure) and the pattern of interference fringes and, consequently, the microstructure may be represented by the equation (2):                     z        =                              f            ⁡                          (                              x                ,                y                            )                                =                      A            ⁡                          [                                                sin                  ⁡                                      (                                          2                      ⁢                      π                      ⁢                                              xe2x80x83                                            ⁢                                              x                        i                                                              )                                                  +                                  sin                  ⁡                                      (                                          2                      ⁢                      π                      ⁢                                              xe2x80x83                                            ⁢                                              y                        i                                                              )                                                              ]                                                          (        2        )            
where i is the period and A the half-amplitude.
In FIG. 1, a system of 90xc2x0-crossed sinusoidal interference fringes is shown.
What has been defined above concerns the case where the pattern of interference fringes is supported by a plane surface.
In the case of a bent surface, the microstructure is slightly distorted with respect to the interference pattern, but does not comprise any abrupt discontinuity.
In particular, the microstructure pitch i may substantially vary depending upon the situation on the correcting surface.
Such distortion can be eliminated by creating a pattern of interference fringes being itself modified to take into consideration the bending of the surface which is to bear the microstructure.
So as to avoid that the cavities in the utility microstructure, in particular the antiglare ones, hold impurities and fats, the microstructure cavities may be filled with a material having a lower refraction index than the microstructure. The index difference for both materials is preferably higher than or equal to 0.1.
An hydrophobic material will preferably be selected as an anti-impurity material.
A convenient anti-impurity material satisfies to the formula: 
where R is an alkyl radical, for example in C1-C6,
and n and nxe2x80x2 are integers which can vary independently from 0 to 6.